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Extraction Well Installation Summary Report and Injection ARCADIS Well Installation Work Plan Former Occidental Chemical Corporation Facility Lathrop, California 2.2.1 Well Installation Well installation was initiated on December 19, 2012 with two drill rigs utilizing sonic drilling methodology at well locations EW-15A and EW-14A. Difficult drilling conditions and heaving sands were encountered, and the drill rigs were unable to advance the casing to the proposed total depth of 155 feet. On January 14, 2013, Cascade switched to mud rotary drilling methods to install the wells initiated with sonic drilling methodology(EW-15A and EW-14A), including the remaining shallow, intermediate, and deep extraction wells(EW-12A, EW-12B, EW-13, EW-14B,and EW-15B). Initial well installations were completed on January 25, 2013. The shallow/intermediate and deep extraction wells were drilled by advancing a 12-inch bit from the ground surface to the total depth of the boring and circulating a water and bentonite mixture with a viscosity of approximately 35 to remove soil cuttings and to prevent the borehole walls from collapsing. Extraction wells EW-12A, EW-13, EW-14A, and EW-15A were drilled to a total depth of approximately 155 feet bgs. Extraction wells EW-126, EW-14B, and EW-15B were drilled to a total depth of approximately 205 feet bgs. Following advancement of the 12-inch bit,the drilling mud used to hold the borehole open was thinned to a targeted viscosity of approximately water and the well materials were placed in the borehole.Well construction details are summarized in Table 1. Extraction wells EW-12A, EW-14A, and EW-15A were screened from approximately 70 to 100 feet bgs and 120 to 150 feet bgs and consist of a 6-inch-diameter 5-foot-long Schedule 80 polyvinyl chloride (PVC)blank sump,followed by 6-inch-diameter stainless steel well screens with 0.010-inch slots at their respective screen intervals. Blank 6-inch-diameter Schedule 80 PVC casing was installed between the upper and lower screens and from the top of the upper screen to approximately the ground surface. After the screen and casing were placed in the open borehole, a sand pack consisting of#2/12 Monterey sand was placed in the borehole to 3 feet above the lower screen; approximately 14 feet of bentonite pellets were placed in the borehole above the lower sand pack and allowed to hydrate. #2/12 Monterey sand was then placed to approximately 3 feet above the upper screen; 3 feet of#0/30 fine transition sand were placed above the sand pack to prevent grout from entering the sand pack.The borehole was then sealed with neat cement grout to 5 feet bgs. Each well was left with a temporary well box and is awaiting vault construction associated with the future expansion of the groundwater treatment system. Extraction well EW-13 was screened from approximately 120 to 150 feet bgs. Extraction wells EW-12B, EW-14B, and EW-15B were screened from approximately 170 to 200 feet bgs. Each well casing consists of a 6-inch-diameter 5-foot-long Schedule 80 PVC blank sump,followed by a 6-inch-diameter stainless steel well screen with 0.010-inch slots,followed by a blank 6-inch-diameter Schedule 80 PVC casing from the top of the screen to approximately the ground surface.After the screen and casing were placed in the open borehole, a sand pack consisting of#2/12 Monterey sand was placed in the lathmp veli installation mpon_fiml_(042913).dmx 3